1. Field of the Invention
The invention relates to a sewing method for sewing (with a sewing machine) a cover material that includes conductive thread.
2. Description of Related Art
One such known cover material is a cover material that can be used as a cover material of a vehicle seat (see Japanese Patent Application Publication No. 2011-243307 (JP 2011-243307 A)). This cover material is a sheet-shaped member of woven fabric or knit fabric or the like that has a plurality of conductive threads woven in (or knitted in) as constituent threads. The plurality of conductive threads extend linearly from one end the other end of the cover material, while being arranged parallel at appropriate intervals. By energizing the plurality of conductive threads, the cover material is able to function as a heater. Also, the cover material (i.e., the conductive thread) is also able to function as an electrode of a capacitance sensor. Here, this kind of cover material is typically made by sewing together a plurality of cover pieces in a bag shape. For example, after preparing the cover pieces by cutting raw fabric, i.e., the woven fabric or the knit fabric, into predetermined shapes, edge portions of adjacent cover pieces are overlapped. Then the overlapping portions are sewn together (i.e., a stitch line formed by a plurality of perforations is formed) by passing a sewing needle through the cover pieces at a predetermined pitch, while moving the cover pieces at a predetermined feed rate with respect to a sewing machine.
In this related art (JP 2011-243307 A), the plurality of conductive threads are arranged linearly from one end to the other end of the cover material (i.e., are arranged at end portions of the cover pieces). Therefore, when the edge portions of the cover pieces are sewn together with the sewing machine, there are cases in which the stitch line formed by a plurality of perforations intersects with the conductive threads or the like, and the conductive threads are broken by the sewing needle. Of course, the sewing needle can be made to pass through positions that differ from the positions where the conductive threads are arranged, by setting the size of the perforations and the like beforehand while taking the interval between the conductive threads into account. However, it is difficult to reliably avoid the conductive threads being broken by the sewing needle because the interval between conductive threads changes (i.e., the conductive threads may be arranged in unexpected positions) due to expansion and contraction of the cover material or the like.